The invention relates to the field of wind turbines for harvesting wind energy. Wind turbines have existed in many different forms since as early as 200 B.C. While other forms of energy generation had reduced the popularity of wind turbines in the recent past, the need for clean, renewable energy sources has sparked renewed interest in the technology.
The efficiency of a wind turbine for harvesting energy is based mainly on the density of the air, the area swept by the rotor, and the wind speed. The useable power available to the turbine from wind action is described by the equationP=½αρπr2v3 where P=power in watts, α=an efficiency factor determined by the design of the turbine, ρ=the mass density of air in kg/cm3, r=the radius of the wind turbine in meters, and v=the velocity of the air in m/s. Betz's law states that α can never be more than 0.59, therefore a wind turbine can extract at most 59% of the energy that flows through its cross section. Betz's limit assumes a perfect disk inside a cylinder of moving air, and thus may possibly be overcome by innovative technology, such as the present invention.
Many different wind turbine designs have been used in the past, both to increase the amount of energy harvested and to improve the reliability of the mechanical parts. The most commonly recognized wind turbine is the windmill, which is a type of horizontal-axis turbine. The windmill has blades which face into the wind and are attached to the top of a tower. A main rotor shaft harvests the wind energy and transfers it to an electrical generator. The main problem with this type of windmill is that the wind passing through the blades creates turbulence. Therefore, the blades must be controlled to maintain them in the direction of the wind. Additionally, turbulence leads to fatigue failures and contributes to maintenance issues with the turbine.
Another type of wind turbine is a vertical-axis turbine, with the rotor shaft in a vertical position. These turbines may use blades or scoops. They have the disadvantage of low energy production because the blades have added drag from the wind as compared to a horizontal-axis turbine.
The currently available wind turbine energy uses the principle of an airfoil, which cuts through the wind. This lowers the amount of wind available for harvesting, creates backflow turbulence, and increases vibration and mechanical fatigue in the turbines.
The present invention overcomes or reduces these issues through its unique design. Instead of blades, the present invention employs a conical helicoid, preferably on a horizontal-axis system, although it may also be mounted on a vertical-axis system. The conical helicoid is comprised of a sail membrane attached to a curved spline ribbing for support. The conical helicoid design results in a high load low rpm wind turbine. The shape reduces backflow turbulences and may possibly allow for harvesting a greater percentage of wind energy than would be predicted by Betz's Law. In addition, because the design works with wind flow instead of cutting through it, maintenance issues should be reduced.
Other advantages of the present invention are that its shape and material components make the conical helicoid safer for wildlife, birds in particular. Birds may be cut by the blades of a typical wind turbine; injury from collision with the conical helicoid would most likely be a stunning type of injury, which is less traumatic. In addition, the conical helicoid's slower speed in revolutions per minute due to its shape is safer for birds as they have more time to react and thus avoid the turbine. The slower rotation rate also may make the present invention quieter than existing turbines.
An additional advantage of the present invention over existing wind turbine technology is reduction of the undesirable ‘strobe effect.’ On a sunny day, the opaque and rapidly moving blades of a traditional wind turbine will produce alternating light and shadows in a strobe pattern. The present invention not only moves more slowly in revolutions per minute, thus dampening the strobe effect, it may also be manufactured of translucent materials that will dampen the effect because the shadows that are created will contrast less with the light.